Hello all-I posted my problem on the Super Duty forum but I thought I might get some other input here so here goes--The parking/running & license plate lights on the back of my 2002 F-350 DRW w/a dump box quit working. Brake lights/turn signals hazards all ok, as are the running lights up front. I have 8 lights total on the back of the truck. I have unwrapped and examined the harness on the dump body and it looks ok. There is a 4 pin plug between the rear crossmember and the fuel tank, not sure if its a factory plug or not. The harness for the dump body plugs into this. Going forward from this plug are 4 wires, one going to the passenger side, and three going to the drivers side. This is where i'm getting confused--the single wire to the passenger side is about 12-18 inches long and goes into another plug, when I unplug this there are four pins inside and one of them is hot when the lights are on, when i plug it back in the single wire is NOT hot. So do I have a bad plug or does the power for the running lights come from the drivers side (I ran out of time before i could check the plug with the three wires) Also what color is the wire that supplies power to the running lights and which side of the truck is it on?? Any help would be great as I have spent about five hours laying on the fuel tank under the raised dump box--plus I can't drive the truck after dark.

 

The difference I see looking at the diagrams is all the rear running lights run through a "trailer tow relay" on a dually truck. This is fed by fuse #17, 15 amp fuse in the underdash fuse box.

The color wire you need to look for is brown. The trailer tow relay is located also in the underdash fuse box. I hope it's not one of those that's built into the fuse box. Someone on here before had a late model truck with trailer lighting problems, and the relay they needed to change was made into the fuse box, and the whole fuse box needed to be replace(another good idea from Ford).

 

I found the broken wire--under the fuel fill pipe about 6 inches from the end of the driverside frame rail in the trucks harness. Took me about 7 hours to find, 5 min to fix and another hour+ to put everything back together. Works fine now--thanks for your help.